1. Field of the Invention
This invention relates in general to a plasma display panel PDP and in particular to an improved trigger electrode circuit for producing an improved plasma display panel.
2. Description of the Prior Art
Plasma display panels of X-Y matrix type are known as a means for displaying characters or images. An X-electrode group which comprises a data electrode may comprise anodes to which high and low voltages are applied corresponding to the display data. A Y-electrode group which may be the scanning electrodes may comprise cathodes which are scanned in a line sequential manner and a negative voltage pulse is applied.
Japanese Patent disclosure number 56-128470 discloses a previously proposed plasma display panel having one or more trigger electrodes in addition to the X-Y electrodes. The trigger electrodes are arranged in the vicinity of the cathodes and are separated from them with an insulating layer. When a high voltage is applied to the trigger electrodes in synchronism with cathode scanning, a trigger discharge which is the inducing discharge is generated between the trigger electrodes and the cathodes. Such inducing discharge permits easy and rapid discharge between the anodes and cathodes so that a drive voltage can be decreased and variations among the discharge cells can be averaged and flickering can be reduced.
The trigger electrodes may be divided into a plurality of phases and the cathodes are divided into groups associated with each trigger electrode phase. When scanning drivers for the cathodes are commonly used among the phases and phase sequential scanning of the trigger electrodes is associated, the number of cathode scanning elements can be decreased to one/(number of phases). Such system is entitled "trigger matrix system" since third matrix electrodes are added to the system.
Such trigger matrix systems are subject to erroneous discharge due to the fact that differences in firing potential and maintaining discharge voltages among discharge cells which can be 10 volts or more can cause misfiring. Once erroneous discharge is generated in one cell it causes a trigger effect which causes sequential generation of erroneous discharges in non-selected cells of other phases. Also, there is a difference of about 10 volts between the discharge self-maintaining voltages at two ends of the panel due to the resistance of the cathode lines. For this reason, there is a margin of variation in the power supply voltage for preventing erroneous discharges which is as small as several volts and stable operation of the display panel over long period of time cannot be easily achieved.
Since potential of the trigger electrodes of the non-selected inactive phases falls to a low voltage such as ground potential an erroneous discharge may be generated between the surface of the trigger dielectric layer of a region of a non-selected phase and the anodes to which data voltages such as high voltage pulses are applied. Light emission due to the erroneous discharge is called "rain discharge" because it appears as a plurality of stripes along a number of anode lines in a vertical display direction. This causes considerable degradation in the display definition. Also, in such prior art display devices, the trigger system requires a large amount of power because the trigger electrodes are capacitive loads and are driven by a high voltage and high frequency pulse. In other words, assuming that there are four hundred cathodes and a frame frequency of 60 Hz a frequency of the cathode is about 24kHz which is about 40 microseconds/line. Since a high voltage pulse of about 300 volts having the same frequency as that of the cathode scanning must be applied to the trigger electrodes and since the trigger electrodes have capacitive loads as mentioned above the trigger circuit requires several tens of watts of power.
Since the trigger electrodes are mounted adjacent the cathode and with a very thin dielectric insulating layer separating them dielectric breakdown can easily occur.